R: Replace “+” character with gsub

问题

the question seems totally trivial but I cannot figure out why it isn't working. I simply want to replace a character variable involving a "+" operator with a single value excluding the "+" operator. For some reason gsub() and sub() function replace the number value but keep the operator. Any hint on how this can be overcome? Many thanks!

data <- c(1,2,3,4,"5+")
gsub(pattern="5+",replacement="5",x=data)
#[1] "1"  "2"  "3"  "4"  "5+"

gsub(pattern="5+",replacement="",x=data)
#[1] "1"  "2"  "3"  "4"  "+"

R 3.0.2

回答1:

+ is a metacharacter, and needs to be escaped when you want to match it:

gsub(pattern="5\\+",replacement="5",x=data)
#[1] "1" "2" "3" "4" "5"

Or more generally, if you want to remove the +:

gsub(pattern="\\+",replacement="",x=data)

If unescaped, + means "The preceding item will be matched one or more times", so in your second example, the "5" element of "5+" is matched by the pattern, and replaced by "", leaving you with "+".

回答2:

Use fixed=TRUE option:

gsub(pattern="+", replacement="", fixed=TRUE, c(1,2,3,4,"5+"))

回答3:

You can also use strsplit:

as.numeric(strsplit(data, "\\+"))
# [1] 1 2 3 4 5

来源：https://stackoverflow.com/questions/20046526/r-replace-character-with-gsub